The long-term goal of the proposed research is to disclose the physiological factors involved in the etiology and the subsequent development and variation of the freemartin syndrome; and to contribute to a further understanding of the role of these factors in the normal and aberrant differentiation of sex in mammals, through the experimental induction of freemartins in the sheep, Ovis aries. Attempts to determine the critical period for freemartin induction will be made utilizing intrauterine surgery to experimentally induce choriovascular anastomosis between adjacent fetuses in superovulated ewes. On day 13 of the estrus cycle, 1000 I.U. PMSG was administered and at the following estrus the ewes were mated to induce multiple embryos. Midline ventral laporotomies were made when the ewes were 28-40 days pregnant and the uteri were exteriorized. Attempts were made to induce fusion of chorio-allantoic membranes across the septum between the uterine horns by removing a section of the uterine wall. Successful fusion has not been accomplished. Future attempts will involve earlier embryos and transplants of testicular tissue and infusion of embryonic blood elements to determine whether experimental induction of freemartinism can be accomplished.